0:14Skip to 0 minutes and 14 secondsScience is a truth-directed practice. Its point is to arrive at true beliefs about the natural world. Once we see that, we can see why scientific and logical and critical thinking should complement one another. As we said, scientific thinking is a subset of logical and critical thinking. And so scientific thinking faces much the same obstacles as logical and critical thinking in general. Science has developed institutional or structural responses to many of those obstacles. Scientific practice, that is, includes particular processes and methods designed specifically to remove the influence of at least the more common and serious obstacles to good logical and critical thinking as done by scientists. Perhaps the most powerful of these institutional responses is the random controlled trial.

1:13Skip to 1 minute and 13 secondsRandom controlled trials randomly assign subjects into experimental and control groups. For simplicity, we're going to assume that there are just two groups, but there might be more. The two groups should be as similar as possible. And once in the trial, the subjects will be treated as similarly as possible except for the treatment or intervention which is being studied. In a simple trial, the experimental group receives the intervention while the control group does not. The idea of course, is that if there are any difference in responses between the groups, they can be attributed to the treatment or the intervention since everything else is meant to have been equal between the two groups.

1:56Skip to 1 minute and 56 secondsThe primary goal of a random controlled trial is to test whether an intervention works by comparing it to a control condition, usually either no intervention or to an alternative intervention. So random controlled trials are importantly focused on the core concerns of science. They allow scientists to be confident that it was their intervention that made the difference and not some other confounding property of the study populations. But they also have direct relevance to our concerns for good logical and critical thinking. Randomisation minimises the influence of confounding factors. But it also prevents researchers from influencing results by, for instance, picking patients for the experimental group who are more likely to respond to treatment in a medical trial. Why would they do that?

2:48Skip to 2 minutes and 48 secondsWell, there's an obvious answer-- if the researcher worked for a pharmaceutical company who has a financial interest in a positive result. In other cases, a medical researcher may have spent her entire career working to find a cure for some condition. They may really hope a treatment will work and might be tempted to offer that treatment to those who have less severe disease or some other factor that might improve the drugs chances of success. We've seen that many of the possible biases here operate at a subconscious level.

3:21Skip to 3 minutes and 21 secondsSo even doctors who are trying to do the right thing might be led to allocate patients in ways which don't give an even baseline, which don't divide the study population randomly between the experimental and control groups. The same sorts of influences which might corrupt selection might also affect the interpretation of results. And so many random controlled trials are blinded. In a blinded trial, the people looking at the results don't know whether the subject is in the study or the control group. So they can't be influenced by preconceived ideas. Remember the problems about confirmation bias and fingerprints. These problems aren't restricted to researchers or doctors. Subjects themselves come up against our familiar obstacles.

4:09Skip to 4 minutes and 9 secondsRecall bias influences the way in which participants report past history and symptoms. If someone knows they're in a placebo group which received no treatment, they may exaggerate their untreated symptoms. They notice those symptoms in a way they wouldn't if they didn't know whether they were in the treatment or the non-treatment arm. Those sorts of problems are usually dealt with by double blinding studies so that neither the participants nor the researchers know whether a particular subject is in the experimental or the control group. And because there are other obstacles to effective scientific thinking, there are other methodological responses designed to ensure that science is as a whole truth-directed.

4:55Skip to 4 minutes and 55 secondsBefore random controlled trials start, for instance, there may be efforts to make sure that the people who enrolled in a trial before randomisation are representative of the population as a whole. If participants are recruited from a student population, for instance, they may tend to be younger than the population average. And so it may not tell you much about what your intervention will do among a more typical population. Or if you recruit by offering money, you may end up with a poorer than average population. And that may have implications for the generalisability of your results.

Random controlled trials

Scientific thinking faces much the same obstacles as logical and critical thinking in general. Science has developed institutional or structural responses to many of those obstacles. Scientific practice, that is, includes particular processes and methods designed specifically to remove the influence of at least the more common and serious obstacles to good logical and critical thinking as done by scientists. Perhaps the most powerful of these institutional responses is the random controlled trial.